The File class extends the FileReference class. The FileReference
class, which is available in Adobe® Flash® Player as well as AIR, represents a pointer
to a file. The File class adds properties and methods that are not exposed
in Flash Player (in a SWF file running in a browser), due to security considerations.

About the File class

You can use the File class for the following:

Getting the path to special directories, including the
user directory, the user's documents directory, the directory from
which the application was launched, and the application directory

Coping files and directories

Moving files and directories

Deleting files and directories (or moving them to the trash)

Listing files and directories contained in a directory

Creating temporary files and folders

Once a File object points to a file path, you can use it to read
and write file data, using the FileStream class.

A File object can point to the path of a file or directory that
does not yet exist. You can use such a File object in creating a
file or directory.

Paths of File objects

Each File object has two properties that each define its path:

Property

Description

nativePath

Specifies the platform-specific path to
a file. For example, on Windows a path might be "c:\Sample directory\test.txt"
whereas on Mac OS it could be "/Sample directory/test.txt". A nativePath property
uses the backslash (\) character as the directory separator character
on Windows, and it uses the forward slash (/) character on Mac OS
and Linux.

url

This may use the file URL scheme to point
to a file. For example, on Windows a path might be "file:///c:/Sample%20directory/test.txt"
whereas on Mac OS it could be "file:///Sample%20directory/test.txt".
The runtime includes other special URL schemes besides file and
are described in Supported AIR URL schemes

The File class includes static properties for pointing to standard
directories on Mac OS, Windows, and Linux. These properties include:

File.applicationStorageDirectory—a
storage directory unique to each installed AIR application. This directory
is an appropriate place to store dynamic application assets and
user preferences. Consider storing large amounts of data elsewhere.

On
Android and iOS, the application storage directory is removed when
the application is uninstalled or the user chooses to clear application
data, but this is not the case on other platforms.

File.applicationDirectory—the directory
where the application is installed (along with any installed assets). On
some operating systems, the application is stored in a single package
file rather than a physical directory. In this case, the contents
may not be accessible using the native path. The application directory
is read-only.

File.desktopDirectory—the user’s desktop
directory. If a platform does not define a desktop directory, another location
on the file system is used.

File.documentsDirectory—the user’s documents
directory. If a platform does not define a documents directory, another
location on the file system is used.

File.userDirectory—the user directory. If
a platform does not define a user directory, another location on
the file system is used.

Note: When a platform does not define standard locations for desktop, documents,
or user directories, File.documentsDirectory, File.desktopDirectory,
and File.userDirectory can reference the same directory.

These properties have different values on different operating
systems. For example, Mac and Windows each have a different native
path to the user’s desktop directory. However, the File.desktopDirectory property
points to an appropriate directory path on every platform. To write
applications that work well across platforms, use these properties
as the basis for referencing other directories and files used by
the application. Then use the resolvePath() method
to refine the path. For example, this code points to the preferences.xml
file in the application storage directory:

Although the File class lets you point to a specific file path,
doing so can lead to applications that do not work across platforms.
For example, the path C:\Documents and Settings\joe\ only works
on Windows. For these reasons, it is best to use the static properties
of the File class, such as File.documentsDirectory.

The actual native paths for these directories vary based on the
operating system and computer configuration. The paths shown in
this table are typical examples. You should always use the appropriate
static File class properties to refer to these directories so that
your application works correctly on any platform. In an actual AIR
application, the values for applicationID and filename shown
in the table are taken from the application descriptor. If you specify
a publisher ID in the application descriptor, then the publisher
ID is appended to the application ID in these paths. The value for userName is
the account name of the installing user.

Pointing a File object to a directory

There
are different ways to set a File object to point to a directory.

Pointing to the user’s home directory

You can point a File object to the user’s home directory. The
following code sets a File object to point to an AIR Test subdirectory
of the home directory:

var file:File = File.userDirectory.resolvePath("AIR Test");

Pointing to the user’s documents directory

You can point a File object to the user's documents directory.
The following code sets a File object to point to an AIR Test subdirectory
of the documents directory:

var file:File = File.documentsDirectory.resolvePath("AIR Test");

Pointing to the desktop directory

You can point a File object to the desktop. The following code
sets a File object to point to an AIR Test subdirectory of the desktop:

var file:File = File.desktopDirectory.resolvePath("AIR Test");

Pointing to the application storage directory

You can point a File object to the application storage directory.
For every AIR application, there is a unique associated path that
defines the application storage directory. This directory is unique
to each application and user. You can use this directory to store
user-specific, application-specific data (such as user data or preferences
files). For example, the following code points a File object to a
preferences file, prefs.xml, contained in the application storage
directory:

The application storage directory location is typically based
on the user name and the application ID. The following file system
locations are given here to help you debug your application. You
should always use the File.applicationStorage property
or app-storage: URI scheme to resolve files in
this directory:

AIR 3.3 and later: path/Library/Application Support/applicationID/Local Store,
where path is either /Users/username/Library/Containers/bundle-id/Data (sandboxed
environment) or /Users/username ( when running
outside a sandboxed environment)

Pointing to the application directory

You can point a File object to the directory in which the application
was installed, known as the application directory. You can reference
this directory using the File.applicationDirectory property. You
can use this directory to examine the application descriptor file
or other resources installed with the application. For example,
the following code points a File object to a directory named images in
the application directory:

Note: On
Android, the files in the application package are not accessible
via the nativePath. The nativePath property
is an empty string. Always use the URL to access files in the application
directory rather than a native path.

Pointing to the cache directory

You can point a File object to the operating system’s temporary
or cache directory using the File.cacheDirectory property. This
directory contains temporary files that are not required for the
application to run and will not cause problems or data loss for
the user if they are deleted.

In most operating systems the cache directory is a temporary
directory. On iOS, the cache directory corresponds to the application
library’s Caches directory. Files in this directory are not backed
up to online storage, and can potentially be deleted by the operating
system if the device’s available storage space is too low. For more
information, see Controlling file backup and caching.

Pointing to the file system root

The File.getRootDirectories() method lists all
root volumes, such as C: and mounted volumes, on a Windows computer.
On Mac OS and Linux, this method always returns the unique root
directory for the machine (the "/" directory). The StorageVolumeInfo.getStorageVolumes() method
provides more detailed information on mounted storage volumes (see Working with storage volumes).

Note: The
root of the file system is not readable on Android. A File object
referencing the directory with the native path, “/”, is returned,
but the properties of that object do not have accurate values. For example, spaceAvailable is
always 0.

Pointing to an explicit directory

You can point the File object to an explicit directory by setting
the nativePath property of the File object, as
in the following example (on Windows):

var file:File = new File();
file.nativePath = "C:\\AIR Test";

Important: Pointing to an explicit path this way can lead
to code that does not work across platforms. For example, the previous
example only works on Windows. You can use the static properties
of the File object, such as File.applicationStorageDirectory,
to locate a directory that works cross-platform. Then use the resolvePath() method
(see the next section) to navigate to a relative path.

Navigating to relative paths

You can use the resolvePath() method to obtain a
path relative to another given path. For example, the following
code sets a File object to point to an "AIR Test" subdirectory of
the user's home directory:

Letting the user browse to select a directory

The File class includes the browseForDirectory() method,
which presents a system dialog box in which the user can select
a directory to assign to the object. The browseForDirectory() method
is asynchronous. The File object dispatches a select event
if the user selects a directory and clicks the Open button, or it
dispatches a cancel event if the user clicks the
Cancel button.

For example, the following code lets the user select a directory
and outputs the directory path upon selection:

Note: On
Android, the browseForDirectory() method is not
supported. Calling this method has no effect; a cancel event is
dispatched immediately. To allow users to select a directory, use
a custom, application-defined dialog, instead.

Pointing to the directory from which the application was invoked

You can get the directory location from which an application
is invoked, by checking the currentDirectory property
of the InvokeEvent object dispatched when the application is invoked.
For details, see Capturing command line arguments.

Pointing a File object to a file

There are different
ways to set the file to which a File object points.

Pointing to an explicit file path

Important: Pointing to an explicit path can lead to code
that does not work across platforms. For example, the path C:/foo.txt
only works on Windows. You can use the static properties of the
File object, such as File.applicationStorageDirectory,
to locate a directory that works cross-platform. Then use the resolvePath() method
(see Modifying File paths) to navigate to a relative path.

You can use the url property of a File object
to point it to a file or directory based on a URL string, as in
the following:

You can also use the nativePath property of
a File object to set an explicit path. For example, the following
code, when run on a Windows computer, sets a File object to the
test.txt file in the AIR Test subdirectory of the C: drive:

var file:File = new File();
file.nativePath = "C:/AIR Test/test.txt";

You can also pass this path to the File() constructor function,
as in the following:

var file:File = new File("C:/AIR Test/test.txt");

Use
the forward slash (/) character as the path delimiter for the nativePath property.
On Windows, you can also use the backslash (\) character, but doing
so leads to applications that do not work across platforms.

Enumerating files in a directory

You can use the getDirectoryListing() method
of a File object to get an array of File objects pointing to files
and subdirectories at the root level of a directory. For more information,
see Enumerating directories.

Letting the user browse to select a file

The
File class includes the following methods that present a system
dialog box in which the user can select a file to assign to the
object:

browseForOpen()

browseForSave()

browseForOpenMultiple()

These methods are each asynchronous. The browseForOpen() and browseForSave() methods
dispatch the select event when the user selects a file (or a target
path, in the case of browseForSave()). With the browseForOpen() and browseForSave() methods,
upon selection the target File object points to the selected files.
The browseForOpenMultiple() method dispatches a selectMultiple event
when the user selects files. The selectMultiple event
is of type FileListEvent, which has a files property
that is an array of File objects (pointing to the selected files).

For example, the following code presents the user with an “Open”
dialog box in which the user can select a file:

If the application has another browser dialog box open when you
call a browse method, the runtime throws an Error exception.

Note: On
Android, only image, video, and audio files can be selected with
the browseForOpen() and browseForOpenMultiple() methods.
The browseForSave() dialog also displays only media files even though
the user can enter an arbitrary filename. For opening and saving
non-media files, you should consider using custom dialogs instead
of these methods.

Modifying File paths

You
can also modify the path of an existing File object by calling the resolvePath() method
or by modifying the nativePath or url property
of the object, as in the following examples (on Windows):

When using the nativePath property, use the forward
slash (/) character as the directory separator character. On Windows,
you can use the backslash (\) character as well, but you should
not do so, as it leads to code that does not work cross-platform.

Supported AIR URL schemes

In
AIR, you can use any of the following URL schemes in defining the url property
of a File object:

URL scheme

Description

file

Use to specify a path relative to the root
of the file system. For example:

file:///c:/AIR Test/test.txt

The
URL standard specifies that a file URL takes the form file://<host>/<path>.
As a special case,<host> can be the empty
string, which is interpreted as "the machine from which the URL
is being interpreted." For this reason, file URLs often have three
slashes (///).

app

Use to specify a path relative to the root
directory of the installed application (the directory that contains
the application.xml file for the installed application). For example,
the following path points to an images subdirectory of the directory
of the installed application:

app:/images

app-storage

Use to specify a path relative to the application
store directory. For each installed application, AIR defines a unique
application store directory, which is a useful place to store data
specific to that application. For example, the following path points
to a prefs.xml file in a settings subdirectory of the application store
directory:

app-storage:/settings/prefs.xml

Controlling file backup and caching

Certain operating systems, most notably iOS and Mac OS X, provide
users the ability to automatically back up application files to
a remote storage. In addition, on iOS there are restrictions on
whether files can be backed up and also where files of different
purposes can be stored.

The following summarize how to comply with Apple’s guidelines
for file backup and storage. For further information see the next
sections.

To specify that a file does not need to be backed up
and (iOS only) can be deleted by the operating system if device
storage space runs low, save the file in the cache directory (File.cacheDirectory).
This is the preferred storage location on iOS and should be used
for most files that can be regenerated or re-downloaded.

To specify that a file does not need to be backed up, but
should not be deleted by the operating system, save the file in
one of the application library directories such as the application
storage directory (File.applicationStorageDirectory)
or the documents directory (File.documentsDirectory).
Set the File object’s preventBackup property to true.
This is required by Apple for content that can be regenerated or
downloaded again, but which is required for proper functioning of
your application during offline use.

Specifying files for backup

In order to
save backup space and reduce network bandwidth use, Apple’s guidelines
for iOS and Mac applications specify that only files that contain
user-entered data or data that otherwise can’t be regenerated or
re-downloaded should be designated for backup.

By default
all files in the application library folders are backed up. On Mac
OS X this is the application storage directory. On iOS, this includes
the application storage directory, the application directory, the
desktop directory, documents directory, and user directory (because
those directories are mapped to application library folders on iOS).
Consequently, any files in those directories are backed up to server
storage by default.

If you are saving a file in one of those
locations that can be re-created by your application, you should
flag the file so the operating system knows not to back it up. To
indicate that a file should not be backed up, set the File object’s preventBackup property
to true.

Note that on iOS, for a file in
any of the application library folders, even if the file’s preventBackup property
is set to true the file is flagged as a persistent
file that the operating system shouldn’t delete.

Controlling file caching and deletion

Apple’s
guidelines for iOS applications specify that as much as possible, content
that can be regenerated should be made available to the operating system
to delete in case the device runs low on storage space.

On
iOS, files in the application library folders (such as the application
storage directory or the documents directory) are flagged as permanent
and are not deleted by the operating system.

Save files that
can be regenerated by the application and are safe to delete in
case of low storage space in the application cache directory. You
access the cache directory using the File.cacheDirectory static
property.

On iOS the cache directory corresponds to the application’s
cache directory (<Application Home>/Library/Caches). On other
operating systems, this directory is mapped to a comparable directory.
For example, on Mac OS X it also maps to the Caches directory in
the application library. On Android the cache directory maps to
the application’s cache directory. On Windows, the cache directory
maps to the operating system temp directory. On both Android and Windows,
this is the same directory that is accessed by a call to the File
class’s createTempDirectory() and createTempFile() methods.

Finding the relative path between two files

You can use the getRelativePath() method
to find the relative path between two files:

The canonicalize() method converts the nativePath object
to use the correct capitalization for the file or directory name.
On case sensitive file systems (such as Linux), when multiple files
exists with names differing only in case, the canonicalize() method
adjusts the path to match the first file found (in an order determined
by the file system).

You can also use the canonicalize() method to convert
short file names ("8.3" names) to long file names on Windows, as
in the following examples:

Working with packages and symbolic links

Various operating systems support package files and symbolic
link files:

Packages—On Mac OS, directories can be designated
as packages and show up in the Mac OS Finder as a single file rather
than as a directory.

Symbolic links—Mac OS, Linux, and Windows Vista support
symbolic links. Symbolic links allow a file to point to another
file or directory on disk. Although similar, symbolic links are
not the same as aliases. An alias is always reported as a file (rather
than a directory), and reading or writing to an alias or shortcut
never affects the original file or directory that it points to. On
the other hand, a symbolic link behaves exactly like the file or
directory it points to. It can be reported as a file or a directory,
and reading or writing to a symbolic link affects the file or directory
that it points to, not the symbolic link itself. Additionally, on
Windows the isSymbolicLink property for a File
object referencing a junction point (used in the NTFS file system)
is set to true.

The File class includes the isPackage and isSymbolicLink properties
for checking if a File object references a package or symbolic link.

The following code iterates through the user’s desktop directory,
listing subdirectories that are not packages:

The canonicalize() method changes the path of a
symbolic link to point to the file or directory to which the link
refers. The following code iterates through the user’s desktop directory,
and reports the paths referenced by files that are symbolic links:

Determining space available on a volume

The spaceAvailable property
of a File object is the space available for use at the File location,
in bytes. For example, the following code checks the space available
in the application storage directory:

trace(File.applicationStorageDirectory.spaceAvailable);

If the File object references a directory, the spaceAvailable property
indicates the space in the directory that files can use. If the
File object references a file, the spaceAvailable property
indicates the space into which the file could grow. If the file
location does not exist, the spaceAvailable property
is set to 0. If the File object references a symbolic link, the spaceAvailable property
is set to space available at the location the symbolic link points
to.

Typically the space available for a directory or file is the
same as the space available on the volume containing the directory
or file. However, space available can take into account quotas and
per-directory limits.

Adding a file or directory to a volume generally requires more
space than the actual size of the file or the size of the contents
of the directory. For example, the operating system may require
more space to store index information. Or the disk sectors required
may use additional space. Also, available space changes dynamically.
So, you cannot expect to allocate all of the reported space for
file storage. For information on writing to the file system, see Reading and writing files.

The StorageVolumeInfo.getStorageVolumes() method
provides more detailed information on mounted storage volumes (see Working with storage volumes).

Opening files with the default system application

In AIR 2, you can open a file using the application registered
by the operating system to open it. For example, an AIR application
can open a DOC file with the application registered to open it.
Use the openWithDefaultApplication() method of
a File object to open the file. For example, the following code
opens a file named test.doc on the user’s desktop and opens it with
the default application for DOC files:

You cannot use the openWithDefaultApplication() method
with files located in the application directory.

AIR prevents you from using the openWithDefaultApplication() method
to open certain files. On Windows, AIR prevents you from opening
files that have certain filetypes, such as EXE or BAT. On Mac OS
and Linux, AIR prevents you from opening files that will launch
in certain application. (These include Terminal and AppletLauncher
on Mac OS; and csh, bash, or ruby on Linux.) Attempting to open one
of these files using the openWithDefaultApplication() method
results in an exception. For a complete list of prevented filetypes,
see the language reference entry for the File.openWithDefaultApplication() method.

Note: This limitation does not exist for an AIR application installed using
a native installer (an extended desktop application).

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